VitaminWater has been good for Coke's bottom line since the acquisition, with sales rising by a double-digit percentage in the third quarter.

''It truly shocks the conscience that a company like Coke would try to keep customers by selling them a soft drink and telling them it's a vitamin,'' said Stephen Gardner, director of litigation for the group.

Coca-Cola did not immediately return a call seeking comment.

The same advocacy group sued MillerCoors last fall to stop the brewer from selling Sparks, an alcoholic energy drink. Last month the company agreed to remove some stimulants from its formula.